The "Mean Girls" star has been trying to get her acting career back on track since she left rehab last year following a series of legal troubles and battles with substance abuse.
Lohan hopes her theater debut on the London stage will re-establish her as actress, but the pressure to deliver is making her nervous.
She tells MailOnline, "I think it's just the idea of when it starts, on opening night, that's what makes me the most nervous. I'll probably mess up on the first night just out of fear.
"I'm excited about the rehearsals, I'm going to be nervous at first obviously. ... But I think the more I get comfortable on the stage in rehearsals, the better it will be. I'm nervous for the show. I'm scared."
Lohan will begin rehearsing the role of Karen in the play on Aug. 25. The production will open at London's Playhouse Theatre on Sept. 24 and run until November.